Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$100.89	10.190%	$111.1707	$111.17	$111.15	$111.20
Purchase #2	$213.60	5.322%	$224.9678	$224.97	$224.95	$225.00
Purchase #3	$144.53	10.601%	$159.8516	$159.85	$159.85	$159.90
Purchase #4	$30.59	9.531%	$33.5055	$33.51	$33.50	$33.50
Purchase #5	$115.95	6.256%	$123.2038	$123.20	$123.20	$123.20
Purchase #6	$26.82	10.581%	$29.6578	$29.66	$29.65	$29.70
Purchase #7	$218.66	12.653%	$246.327	$246.33	$246.35	$246.30
7 purchase totals =	$851.04		$928.6842	$928.69	$928.65	$928.80